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Influence d'une source prévisible de nourriture anthropogénique sur l'écologie spatiale, la dynamique populationnelle et la conservation d'un prédateur marin

Abstract : Seabirds are flagship species, boundary objects linking air and water, oceans and continents, Northern and Southern countries, binding a great variety of socio-ecosystems across the planet. Due to their ubiquity, they are exposed to numerous global threats. Among them, interactions with fisheries might be the main risk for seabirds at sea. The conservation status of seabirds is thereby affected, and priority actions due to reduce these impacts have to be established. Indeed, seabirds catch the attention of all stakeholders and of the general public, who are sensitive to the fate of their populations. Implementing tools and strategies allowing seabird conservation is therefore an urgent societal request. The Northern gannet (Morus bassanus) is emblematic of seabird conservation in metropolitan France, with a single breeding colony under strict protection within the Réserve Naturelle Nationale de l’archipel des Sept-Îles. Despite all conservation efforts, colony size and breeding success have been declining in recent years. A decadal biotelemetry study allowed us to test hypotheses linked to this decline. Notably, we showed that, during the breeding season, gannets shifted from feeding on natural prey, to taking fisheries waste. The consumption of these anthropogenic subsides affects foraging effort, adult body condition and reproductive output. Further, we showed that, during the inter-breeding period, gannets were exposed to enhanced bycatch risk and competition with fisheries for small pelagic fish. This had a strong impact on adult inter-annual return rates to the colony, potentially explaining the recent decline of the Sept-Îles gannetry. Overall, we conclude that an integrated conservation plan for Northern gannets, as well as for the marine megafauna in general, is only possible through ecosystem-based fisheries management. Specifically, the joint use of fish stocks by marine predators and fisheries should be taken into account by management schemes, at-sea dumping of fishery wastes should be reduced, and marine protected areas including true no-take zones should be designed, also by taking into account the spatial ecology of the marine megafauna such as seabirds.
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Tangi Le Bot. Influence d'une source prévisible de nourriture anthropogénique sur l'écologie spatiale, la dynamique populationnelle et la conservation d'un prédateur marin. Biodiversité et Ecologie. Université Montpellier, 2018. Français. ⟨NNT : 2018MONTG075⟩. ⟨tel-02063432⟩

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